Lots of quadcopter flight controllers use 9DOF IMUs , with 3 gyros, 3 accelerometers, and 3 compasses. The absolute directional data from the compasses solves (at least most of) the angular/gyro drift.
The translational drift is harder for VR/AR headsets indoors. Drones can do sensor fusion with GPS and the accelerometers to solve translational drift from the accelerometers (or, for FPV drones, they just let the meatware compensate).
The "9DoF" in IMU datasheets is a marketing term, they just add up all the sensor dimensions they have.
Some IMU modules talk about "10DoF" , because they have added a barometer to it.
So even a good "9DoF" IMU is not usable for 6DoF VR, as it still drifts way too much.
Sadly the magnetometer in the IMUs suffers from all the magnetic fields generated by the rest of the electronics around it.
This might also be one of the reasons why 9DoF IMUs are increasingly rare on the market.
The translational drift is harder for VR/AR headsets indoors. Drones can do sensor fusion with GPS and the accelerometers to solve translational drift from the accelerometers (or, for FPV drones, they just let the meatware compensate).